Xenotransplantation Science, Ethics, and Public Policy (1996) / Chapter Skim
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3. Infectious Disease Risk to Public Health Posed By Xenografting
3. Infectious Disease Risk to Public Health Posed By Xenografting
Pages 39-56
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From page 39... ...
It is the second step of establishment and dissemination, however, that raises public health concerns, particularly if the agent is viral since current therapies for viral illnesses are limited.
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From page 40... ...
If so, the second question is whether such infections constitute a threat to the general public health rather than a complication limited to the individual xenotransplant recipient. Third, what options are available for the prevention and control of infectious diseases associated with the use of xenogeneic tissue in humans?
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From page 41... ...
Immunosuppression inhibits the development of specific antibodies, thereby increasing the risk of infectious disease for the patient and also hindering some of the usual methods for detecting infectious disease. Recombination of an animal virus from the transplanted organ with a human virus present in the recipient, although perhaps unlikely to occur, is still of concern because such an event could produce a new virus with more pathogenic properties.
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From page 42... ...
Whether these organisms might have more pathogenic potential when transmitted from their natural host across species lines with xenotransplantation is not yet known. BASIS FOR PUBLIC HEALTH CONCERN The second question is whether xenogeneic infections constitute a threat to the general public health or are only a complication of the risk-benef~t calculation for the individual xenotransplant recipient (Chapman, 1995; and Chapman et al., 1995~.
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From page 43... ...
The potential for xenogeneic infections to be transmitted through human populations is real and poses a public health concern. Further, the risk for health care workers in close contact with the xenograft recipient is probably higher than for the community at large.
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From page 44... ...
Baboon retrovirus can be isolated from baboons by cocultivation with human cells. Although no true recombinant of animal endogenous retrovirus with other animal viruses has been described, phenotypic mixing between different viruses can occur under appropriate experimental conditions, which suggests that this and other endogenous retroviruses may have pathogenic potential under conditions associated with xenotransplantation.
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From page 45... ...
First, evidence must be collected on the effects of exposure to a particular microbe by an individual and a population. Second, a risk assessment must be performed that includes three related activities: Hazard identification determines if the microbe actually causes an adverse effect.
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From page 46... ...
Such communication involves relating relative risk and likelihood to common experience as exemplified by the statement "It is safer to fly than it is to drive a car the same distance." Regarding the infectious disease risk to public health posed by xenotransplantation, data are missing on several of the links required to perform an adequate risk assessment. The information summarized in the first portion of this chapter permits identification of some of the known potential hazards and has shown that transmission of microorganisms occurs with xenotransplantation from animals to humans.
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From page 47... ...
The risk of infecting the recipient with previously recognized zoonotic pathogens can be controlled by adequate survey of the animal source, by screening and quarantine the individual animal or developing well-characterized source colonies where feasible, and by attending to the circumstances and methodology of tissue retrieval. Screening should also be performed on the recipient pretransplant (baseline)
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From page 48... ...
When nonhuman primates such as baboons are to be sources of the transplanted material, they should be screened for other organisms that, although unlikely to be found in animals raised in captivity in the United States, would preclude their use as a source of organs. Examples of such organisms include Ebola, Marburg, and Reston, as well as viruses that cause simian hemorrhagic fever and monkey pox.
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From page 49... ...
Public health guidelines exist that are intended to minimize the risk of transmission of known pathogens by human-to-human transplantation, and similar guidelines are under development that address xenotransplantation. In addition, when human infections with known zoonotic pathogens occur, standard diagnostic testing procedures and disease descriptions may be helpful.
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From page 50... ...
In summary, SPF baboons would not be entirely free of infectious agents, would be expensive to produce and maintain, would require considerable time to develop, and would be an economically stressed approach to decreasing the infectious disease potential of baboons at present. If further research shows that baboons are a good source of cells, tissues, or organs for xenotransplantation, it may be worth reconsidering the production of pathogen-free baboons.
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From page 51... ...
Xenotransplant recipients will all have underlying illnesses that set them apart from the normal population prior to transplantation. In this setting, surveillance must monitor for adverse health events that are unexpected, unexplained, possibly infectious, and occurring at a higher than normal rate, which is difficult to determine for a distinctly abnormal population.
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From page 52... ...
Some of the more conventional techniques, such as culture and animal model to create a registry recovery techniques, and the technological framework for some of the nucleic acid techniques are discussed below. Improvements in culture techniques have resulted in the recovery of many organisms not detectable with standard methods, including Legionella pneumophila, Bartonella henselae, Borrelia species, Mycobacterium genevensii, and other pathogens.
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From page 53... ...
A nucleic acid technique called representational difference analysis RDA, based on subtractive hybridization, has been developed.) The RDA technique has been used to identify several organisms including human he~pesvirus 8, which is associated with Kaposi's sarcoma, and a new hepatitis-associated flavivirus.
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From page 54... ...
A xenotransplantation national registry would collect data on xenotransplant recipients that permitted documentation of significant commonalities among them. Such a registry ideally should be able to capture patients' records automatically and electronically, while safeguarding patient identity.
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From page 55... ...
Some types of safeguards must be considered for this mandatory lifelong surveillance, however, because it implies the need for enforcement under some circumstances and presents the possibility of limitations to individual freedom and privacy. Such a national or international registry would allow prospective monitoring of individual xenotransplant recipients and of the recipient population as a whole, as well as retrospective tracking of epidemiologically linked recipients for investigation of adverse events, if they should occur.
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From page 56... ...
Preplanned transplantation screening of the animal that is the source of the graft for known zoonotic pathogens and posttransplantation surveillance of the recipient for adverse health events possibly associated with xenogeneic infections are the best tools available.
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